The invention relates to a method and an apparatus for addressing a central memory for interrogating it with respect to stored data. The addressing takes place in dependence on external and time-dependent operational conditions of the engine which, itself, is controlled by the data contained in the central memory. In addition, one or more of the operational engine conditions may be dependent on other parameters, for example the engine temperature. The method and apparatus according to the invention for addressing a central memory is useful especially when used in connection with an electronic fuel injection system which uses the data in the central memory to generate a correction frequency which it transmits to a central processor for producing control pulses which are used in operating the fuel injection valves of the engine. However, the method and apparatus according to the invention is useful not only in the field of fuel injection but may be used wherever the operation of a system requires control in accordance with operational conditions which may be of very complicated form.
In order to define the duration of the fuel injection control pulses, which, in turn, are a measure of the fuel supplied to the engine, the induction tube manifold of the engine contains an air flow rate meter of any suitable construction and so embodied as to produce an electrical signal as a function of the air flow rate through the induction tube. In order to obtain an approximately stoichiometric fuel mixture, the signal thus produced, which is proportional to the air flow rate, is then divided by the rpm of the crankshaft, i.e., the number of suction strokes per unit time, in order to produce a fuel control datum. For this purpose, in a known fuel injection system in which the length of the pulses is formed by a monostable multivibrator having a capacitor in its feedback path, the capacitor is charged with a constant charging current during a time which is inversely proportional to the crankshaft rpm and is subsequently discharged with an equally fixed discharging current which, however, is inversely proportional to the air flow rate. The duration of the discharge of the capacitor is used as a measure of the duration of the fuel injection pulses. Connected behind this first stage in the known system is a so-called multiplier stage which operates in similar manner as the first monostable flip-flop and which receives correction signals related to other operational conditions of the engine which then are used by the multiplier stage to produce the final injection control pulses t.sub.i. In such known fuel injection systems, there is required an adaptation to the particular type of engine, so that it must be possible to change the system to correspond to the number of cylinders and to permit other adjustments and corrections.
The system according to the present invention relates to an electronic fuel injection system of substantially different construction, being based on digital operation and thus useable for universal applications, for example for generating highly precise injection control pulses for the fuel injection valves of an internal combustion engine. The data associated with a particular internal combustion engine are stored in a central fixed memory and are cyclically interrogated so as to correct the fuel injection control signal. In order to perform this cyclic interrogation and correction, there is required an address computer.